Using electronic scheme in the figure below can be constructed logic tester with acoustic indication. Acoustic tester in the figure below produces a low frequency sound when detects a logic 0, respective high-frequency sound when 1 logic is detected. The frequency produced by capacitors C1 and C2 depends. The input signal is supplied directly to the gate of N2 and reversed at the gate N3. If at input is detected, a logic gate N2 signal to pass through the amplifier A1. If a 0 is detected at input logic gate N3 signal to pass from the amplifier A2.
Using electronic scheme shown below can be made a tester for bipolar transistors. Using this electronic circuit we can sort transistors, depending on the class of amplification (gain in current between 140-270), B (270-500) or C (less than 500).
For proper testing NPN transistor is necessary that the transistor to be inserted into the socket TUT (Transistor Under Test) and turn switch S2 in position C. If the LED does not light move switch S2 in position B, and if does not light even in this position, move the switch S2 on the last position.
A very simple transistor tester electronic circuit project can be designed using this circuit diagram . This transistor tester electronic circuit project is very useful for testing both types of transistors pnp and npn. This transistor tester electronic circuit project is composed from few common electronic parts like : resistors, LEDs and diodes . The circuit is powered from a simple 6 volts unregulated power supply ( you can use a small 6 volts step down transformer) . The tested transistor must be inserted in the EBC terminals of the device ( emitter, base, collector) .